I am about to jump into this remarkable camera line so please forgive my ignorance. I want to focus on the ground class and use a Polaroid Back (550 or 545) Can a Graphic (spring) back take these film holders or do I need to find a camera with a graflok back? It is not 100% clear to me by reading the text and since I'm with the U.S. Navy in Italy I can't just wonder down to a store to look at one.